1. Field of the Invention
The present invention relates to a film formation apparatus and a film formation method employed for film formation of a film formable material (hereinafter, referred to as a deposition material) by deposition. Additionally, the invention relates to a cleaning method for removing a deposition material adhering to the inner wall or the like by the deposition. Particularly, the invention is an efficient technique in the case an organic material is used as the deposition material.
2. Related Art
In recent years, investigations of light emitting apparatuses comprising EL elements as self-luminous type elements have been enthusiastically carried out and specially, light emitting apparatuses using organic materials as EL materials have drawn attention. Such a light emitting apparatus is called as an organic EL display (OELD) or an organic light emitting diode (OLED).
The EL element comprises a layer (hereinafter referred to as an EL layer) containing an organic compound capable of emitting electroluminescence by electric field application, an anode, and a cathode. The luminescence in the organic compound includes light emission (fluorescence) at the time of returning to the normal state from the singlet state and light emission (phosphorescence) at the time of returning to the normal state from triplet state and a light emitting apparatus to be manufactured by the film formation apparatus and the film formation method of the invention is applicable for cases using both fluorescence and phosphorescence.
The light emitting apparatus has a characteristic that it has no problem in the visible angle because it is self-luminous type, not a liquid crystal display apparatus. That is, as a display to be employed outdoors, the apparatus is more suitable than a liquid crystal display and application in various manners has been proposed.
The EL element has a structure in which the EL layer is sandwiched between a pair of electrodes and the EL layer generally has a layered structure. A typical example is a layered structure of a hole transporting layer/a light emitting layer/an electron transporting layer proposed by Tang, Eastman Kodak Co. The structure has a remarkably high light emitting efficiency and almost all of light emitting apparatuses which have been presently investigated and developed employ the structure.
Further, structures of a hole injecting layer/a hole transporting layer/a light emitting layer/an electron transporting layer formed successively on an anode and of a hole injecting layer/a hole transporting layer/a light emitting layer/an electron transporting layer/an electron injecting layer may be employed. A fluorescent coloring material or the like may be doped in the light emitting layers. Further, these layers may be formed by using materials all with low molecular weights or using materials all with high molecular weights.
Incidentally, in the specification, all layers to be formed in a cathode and an anode are generically named as an EL layer. Accordingly, the above-mentioned hole injecting layer, hole transporting layer, light emitting layer, electron transporting layer, electron injecting layer are all included in the EL layer.
Also, in the specification, the light emitting element composed of a cathode, an EL layer, and an anode is called as an EL element and there are two types of the EL element: one is a simple matrix type in which the EL layer is formed between two kinds of stripe-like electrodes formed at right angles to each other and the other is an active matrix type in which the EL layer is formed between pixel electrodes connected to TFT and arranged in a matrix and a counter electrode.
The most important problem of the EL element on practical application is that the life of the element is insufficient. The deterioration of the element appears in a way that a non-light emitting region (a dark spot) is widened as the light emission is carried out for a long time and as a cause of the deterioration, the EL layer deterioration becomes an issue.
The EL materials forming the EL layer are deteriorated by impurities such as oxygen, water and the like. Further, it may be also possible that the deterioration of the EL layer is affected by contamination of the EL materials with other impurities.
Further, the EL materials are divided broadly into low molecular weight (monomer-type) materials and high molecular weight (polymer-type) materials and among them, the low molecular weight materials are mainly formed into films by deposition.
In the case of film formation by a conventional deposition method, a deposition material is used as it is, but the deposition material for the deposition, is supposed to be contaminated with impurities. That is, oxygen, water, and other impurities, which are one of the causes of deterioration of the EL element, are probably mixed therein.
Further, although the purity can be increased by previously refining the deposition material, there is probability that impurities are mixed by the time when evaporation is carried out.
EL materials are extremely susceptible to deterioration and easily oxidized and deteriorated in the presence of oxygen or water. For that, a photolithographic process cannot be carried out after film formation and in order to form a pattern, the film has to be separated using a mask having openings (hereinafter referred to as a deposition mask) simultaneously with film formation. Accordingly, almost all of the sublimated organic EL materials adhere to a deposition mask or a deposition-preventing shield (a protective plate for preventing adhesion of the deposition materials to the inner walls of a film formation chamber) in the film formation chamber.
In order to remove the organic EL materials adhering to the deposition mask or the deposition preventing shield, it is required to open the film formation chamber to the atmospheric air once, take the deposition mask or the deposition preventing shield outside and then return it again to the film formation chamber after washing it. However, water or oxygen adsorbed in the deposition mask or the deposition preventing shield exposed to the atmospheric air may be probable to be isolated and taken in the film at the time of film formation using the organic EL materials and thus it is apprehended that adsorbed water or oxygen may be a factor of promoting deterioration of the organic EL materials.
The invention is achieved in consideration of the above-mentioned problems and has an aim to provide a film formation apparatus capable of forming an EL layer with a high throughput, a high density, and a high purity. Another aim of the invention is to provide a film formation method using the film formation apparatus of the invention.
Additionally, another aim of the invention is to provide a cleaning method for removing deposition materials adhering to jigs installed in the inside of the film formation apparatus of the invention and the inner wall of the film formation apparatus without exposing them to the atmospheric air and to provide a film formation apparatus provided with the mechanism for carrying out the cleaning method. Incidentally, in the specification, the jigs installed in the inside of the foregoing film formation apparatus include a substrate holder, a mask holder, a deposition preventing shield and a deposition mask.
A film formation apparatus of the invention is a film formation apparatus for forming a film on a substrate by depositing an organic compound material from a deposition source installed on the opposite to the substrate; wherein a film formation chamber to install the substrate therein comprises a deposition source, a means for heating the deposition source, and a heating means for heating a mask and the film formation chamber is communicated with a vacuum gas discharge treatment chamber for vacuum evacuating the film formation chamber.
The invention provides a method for forming a highly dense EL layer by heating a substrate by a means for heating the substrate and further decreasing the pressure to 5xc3x9710xe2x88x923 Torr (0.665 Pa) or lower, preferably to 1xc3x9710xe2x88x923 Torr (0.133 Pa) or lower, by a pressure decreasing means (a vacuum pump such as a turbo-molecular pump, a dry pump, a cryopump and the like) connected to the film formation chamber and depositing an organic compound material from the deposition source to carry out film formation. Accordingly, in the invention, annealing can be carried out in vacuum simultaneously with the film formation. Alternatively, the substrate may be annealed in vacuum before the film formation. Also, the substrate may be annealed in vacuum after the film formation. The temperature (T1) of the foregoing substrate is set to be lower than the temperature (T3). Further, as the means for heating the substrate, a stage (optionally having a function of fixing the substrate) in which a heater and an electric heating wire are formed or a metal mask in which a heater and an electric heating wire are formed is used to heat while being installed closely to or in the vicinity of the substrate and the temperature (T1) of the substrate is controlled to be 50 to 200xc2x0 C., preferably 65 to 150xc2x0 C. In the present invention, by heating the substrate, the deposition mask installed closely to or in the vicinity of the heated substrate is also heated. Accordingly, it is preferable for the deposition mask to be made of a metal material (e.g. a high melting point metal such as tungsten, tantalum, chromium, nickel, molybdenum and alloys containing these elements) a stainless steel, Inconel, Hastelloy and the like which are hardly deformed by heating (having a low thermal expansion coefficient) and durable to the temperature (T1) of the substrate. For example, a low thermal expansion alloy (42 alloy) containing nickel 42% by weight and 58% by weight and a low thermal expansion alloy (36 Invar) containing nickel 36% by weight having a thermal expansion coefficient near to that (0.4xc3x9710xe2x88x926 to 8.5xc3x9710xe2x88x926) of a glass substrate can be exemplified.
Further, it is preferable to install an adhesion prevention means for preventing the organic compound from adhering to the inner wall of the film formation chamber at the time of deposition and the film formation apparatus of the invention is a film formation apparatus for forming a film on a substrate by depositing an organic compound material from a deposition source installed on the opposite to the substrate; wherein a film formation chamber to install the substrate therein comprises an adhesion prevention means for preventing film formation in the inner wall, a heating means for heating the adhesion prevention means, the deposition source, a means for heating the deposition source, and a heating means for heating the substrate or a mask (a deposition mask) and the film formation chamber is communicated with a vacuum gas discharge treatment chamber for vacuum evacuating the film formation chamber.
As the adhesion prevention means, a deposition preventing shield is preferable and a heater is installed in the surrounding of the deposition preventing shield to heat the entire body of the deposition preventing shield and set the temperature (T2) of the deposition preventing shield to be higher than the temperature (T1) of the substrate by at least 10xc2x0 C., so that an organic compound which is not deposited on the substrate can be stuck to the substrate. Further, by heating the deposition preventing shield to a certain temperature (the sublimation temperature of the organic compound) or higher, cleaning of the film formation chamber can be carried out by evaporating the adhering organic compound.
In the invention, the temperature (T1) of the substrate at the time of film formation is set to be lower than the temperature (T2) of the deposition preventing shield and the temperature (T2) of the deposition preventing shield is set to be lower than the temperature (T3) of the deposition source. Further, using the film formation apparatus of the invention, an inline-type film formation apparatus can be obtained and such a film formation apparatus of the invention is a film formation apparatus comprising a load chamber, a transportation chamber, and a film formation chamber joined to each other in series; wherein the film formation chamber has a function of conforming the positioning of a mask and a substrate and the film formation chamber is communicated with a vacuum gas discharge treatment chamber for vacuum evacuating the film formation chamber and comprises an adhesion prevention means for preventing film formation in the inner wall, a heating means for heating the adhesion prevention means, the deposition source, a means for heating the deposition source, and a heating means for heating a substrate or a mask (a deposition mask).
Further, using the film formation apparatus of the invention, a multichamber-type film formation apparatus can be obtained and such a film formation apparatus of the invention is a film formation apparatus comprising a load chamber, a transportation chamber, and a film formation chamber joined to each other in series; wherein the transportation chamber has a function of conforming the positioning of a mask and a substrate and the film formation chamber is communicated with a vacuum gas discharge treatment chamber for vacuum evacuating the film formation chamber and the film formation chamber comprises an adhesion prevention means for preventing film formation in the inner wall, a heating means for heating the adhesion prevention means, the deposition source, a means for heating the deposition source, and a heating means for heating a substrate or a mask (a deposition mask).
In the above-mentioned respective film formation apparatuses, a plurality of deposition sources are arranged in one film formation chamber and in a single film formation chamber, a plurality of functional regions can be formed and thus a light emitting element having mixed regions can be formed. Accordingly, in the case an organic compound film comprising a plurality of functional regions is formed between an anode and a cathode of a light emitting element, unlike a conventional layered structure in which clear interfaces exist, a structure in which a mixed region of both of a material composing a first functional region and a material composing a second functional region is formed between the first functional region and the second functional region can be formed. In accordance with the invention, before the film formation or during the film formation, vacuum annealing is carried out, so that molecules in the mixed region can be fitted better with one another. Formation of the mixed region moderates the energy barrier between functional regions. Consequently, the driving voltage can be lowered and the deterioration of brightness can be prevented.
The first organic compound and the second organic compound have properties selected from a group consisting of a hole injecting property to receive hole from an anode, a hole transporting property with higher hole mobility than electron mobility, an electron transporting property with higher electron mobility than hole mobility, an electron injecting property to receive electron from a cathode, a blocking property to inhibit hole or electron transportation, and a light emitting property showing luminescence and respectively have different properties.
As the organic compound with a high hole injecting property, a phthalocyanine type compound is preferable and as the organic compound with a high hole transporting property, an aromatic diamine compound is preferable and as an organic compound with a high electron transporting property, a metal complex containing a quinoline skeleton, a metal complex containing a benzoquinoline skeleton, an oxadiazole derivative, a triazole derivative, or a phenanthroline derivative is preferable. Further, as an organic compound showing luminescence, a metal complex containing a quinoline skeleton, a metal complex containing a benzoxazole skeleton, or a metal complex containing a benzothiazole skeleton, which is capable of stably emitting luminescence, is preferable.
Further preferably, a light emitting region is composed of a host material and a light emitting material (a dopant) whose excitation energy is lower than that of the host material and the excitation energy of the dopant is planed to be lower than the excitation energy of a hole transporting region and the excitation energy of the electron transporting layer. Due to that, dispersion of excited molecules of a dopant can be prevented and the dopant can efficiently emit luminescence. Further, in the case a dopant is a carrier trap type material, the re-coupling efficiency of the carrier can be heightened.
Further, the invention includes a case that as a dopant, a material capable of converting triplet excitation energy to luminescence is added to the mixed region. In the mixed region formation, the mixed region may have a concentration grade.
The film formation apparatus of the invention can be employed for film formation of not only an organic compound such as the EL material but also other materials such as metal materials to be employed for deposition.
Further, by radiating laser beam and scanning the laser beam in the inner wall of the film formation chamber, cleaning can be carried out and thus the film formation apparatus of the invention includes a film formation apparatus for forming a film on a substrate by depositing an organic compound material from a deposition source installed on the opposite to the substrate; wherein a film formation chamber to install the substrate therein comprises a deposition source, a means for heating the deposition source, and a heating means for heating a substrate, and the film formation chamber is communicated with a vacuum gas discharge treatment chamber for vacuum evacuating the film formation chamber and also with a cleaning preparatory chamber for radiating laser beam to the inner wall of the treatment chamber.
In the foregoing constitution, the above-mentioned laser beam can be scanned by a galvano-mirror or a polygon mirror to evaporate the deposited matter adhering to the inner wall of the film formation chamber, a deposition preventing shield, or a deposition mask and carry out cleaning. With the above-mentioned constitution, without the film formation chamber being exposed to atmospheric air at the time of maintenance, cleaning can be carried out.
The above-mentioned laser beam may include laser beam from laser beam source such as continuously oscillating or pulse oscillating solid laser, continuously oscillating or pulse oscillating excimer laser, Ar laser, Kr laser and the like. The above-mentioned solid laser includes one or a plurality of types selected from YAG laser, YVO4 laser, YLF laser, YAlO3 laser, glass laser, ruby laser, alexandrite laser, Ti:sapphire laser.
Further, a film formation apparatus having a plasma generation means in a film formation apparatus provided with a deposition source is also among the invention and another constitution regarding the film formation apparatus of the invention is a film formation apparatus for forming a film on a substrate by depositing an organic compound material from a deposition source installed on the opposite to the substrate; wherein a film formation chamber to install said substrate therein comprises a deposition source, a means for heating the deposition source, a heating means for heating a substrate, a mask (a deposition mask), and an electrode on the opposite to the mask and the film formation chamber is communicated with a vacuum gas discharge treatment chamber for vacuum evacuating the film formation chamber and plasma is generated in the film formation chamber.
In the above-mentioned constitution, the foregoing mask is made of a conductive material and either the foregoing mask or the foregoing electrode is connected with a high frequency power source (frequency of 13 MHz to 40 MHz and high frequency power 20 W to 200 W). The interval of the mask and the electrode may be adjusted to be 1 cm to 5 cm. Also, in the above-mentioned constitution, the foregoing film formation chamber is provided with a gas introducing means for introducing one or a plurality of kinds of gases selected from Ar, H, F, NF3, and O into the film formation chamber and a means for discharging the evaporated deposition substance.
Further, in the above-mentioned constitution, it is preferable that the deposition mask to be one electrode for generating plasma is made of a material having conductivity and a high melting point metal such as tungsten, tantalum, chromium, nickel, molybdenum and alloys containing these elements) a stainless steel, Inconel, Hastelloy and the like which are hardly deformed by heating (having a low thermal expansion coefficient) and durable to plasma is preferable to be employed. Further, in order to cool the heated deposition mask, a mechanism for circulating a cooling medium (cooling water, cooling gas) in the deposition mask may be installed.
By the above-mentioned plasma generating means, plasma is generated in the film formation chamber and the deposited substance adhering to the inner wall of the film formation chamber, the deposition-preventing shield, or the deposition mask is evaporated and discharged out the film formation chamber to carry out cleaning. With the above-mentioned constitution, cleaning can be carried out without the film formation chamber being exposed to the atmospheric air at the time of maintenance.
The cleaning method using the film formation apparatus with the above-mentioned constitution is also included in the invention and a cleaning method for removing an organic compound adhering to a film formation chamber provided with a deposition source and carried out for cleaning the inner wall, an adhesion prevention means for preventing film formation on the inner wall, or a mask by generating plasma in the film formation chamber.
In the constitution of the above-mentioned cleaning method, the foregoing plasma is generated between the mask and an electrodes installed between the mask and the deposition source.
In the constitution of the above-mentioned cleaning method, the plasma is generated by exciting one or a plurality of kinds of gases selected from Ar, H, F, NF3, and O.